9 files changed, 31 insertions, 16 deletions
diff --git a/examples/rust/Cargo.toml b/examples/rust/Cargo.toml
index 5c6b710..da238ad 100644
--- a/examples/rust/Cargo.toml
+++ b/examples/rust/Cargo.toml
@@ -23,6 +23,10 @@ name="hello"
 path="src/hello.rs"
 
 [[bin]]
+name="host_fn"
+path="src/host_fn.rs"
+
+[[bin]]
 name="print"
 path="src/print.rs"
 
diff --git a/examples/rust/build.sh b/examples/rust/build.sh
index d0415ac..e1d320f 100755
--- a/examples/rust/build.sh
+++ b/examples/rust/build.sh
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
-cd "$(dirname "$0")"
+cd "$(dirname "$0")" || exit
 
-bins=("hello" "fibonacci" "print" "tinywasm" "argon2id")
+bins=("host_fn" "hello" "fibonacci" "print" "tinywasm" "argon2id")
 exclude_wat=("tinywasm")
 out_dir="./target/wasm32-unknown-unknown/wasm"
 dest_dir="out"
diff --git a/examples/rust/src/argon2id.rs b/examples/rust/src/argon2id.rs
index 01ea7ca..ff17d04 100644
--- a/examples/rust/src/argon2id.rs
+++ b/examples/rust/src/argon2id.rs
@@ -1,6 +1,6 @@
 #![no_main]
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn argon2id(m_cost: i32, t_cost: i32, p_cost: i32) -> i32 {
     let password = b"password";
     let salt = b"some random salt";
diff --git a/examples/rust/src/fibonacci.rs b/examples/rust/src/fibonacci.rs
index b847ad5..ec4a371 100644
--- a/examples/rust/src/fibonacci.rs
+++ b/examples/rust/src/fibonacci.rs
@@ -1,6 +1,6 @@
 #![no_main]
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn fibonacci(n: i32) -> i32 {
     let mut sum = 0;
     let mut last = 0;
@@ -13,7 +13,7 @@ pub extern "C" fn fibonacci(n: i32) -> i32 {
     sum
 }
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn fibonacci_recursive(n: i32) -> i32 {
     if n <= 1 {
         return n;
diff --git a/examples/rust/src/hello.rs b/examples/rust/src/hello.rs
index c8e2ac3..3d9f400 100644
--- a/examples/rust/src/hello.rs
+++ b/examples/rust/src/hello.rs
@@ -1,23 +1,23 @@
 #![no_main]
 
 #[link(wasm_import_module = "env")]
-extern "C" {
+unsafe extern "C" {
     fn print_utf8(location: i64, len: i32);
 }
 
 const ARG: &[u8] = &[0u8; 100];
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub unsafe extern "C" fn arg_ptr() -> i32 {
     ARG.as_ptr() as i32
 }
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub unsafe extern "C" fn arg_size() -> i32 {
     ARG.len() as i32
 }
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub unsafe extern "C" fn hello(len: i32) {
     let arg = core::str::from_utf8(&ARG[0..len as usize]).unwrap();
     let res = format!("Hello, {}!", arg).as_bytes().to_vec();
diff --git a/examples/rust/src/host_fn.rs b/examples/rust/src/host_fn.rs
new file mode 100644
index 0000000..ada74bd
--- /dev/null
+++ b/examples/rust/src/host_fn.rs
@@ -0,0 +1,11 @@
+#![no_main]
+
+#[link(wasm_import_module = "env")]
+unsafe extern "C" {
+    fn bar(left: i64, right: i32) -> i32;
+}
+
+#[unsafe(no_mangle)]
+pub fn foo() -> i32 {
+    unsafe { bar(1, 2) }
+}
diff --git a/examples/rust/src/print.rs b/examples/rust/src/print.rs
index d04daa3..d2934f0 100644
--- a/examples/rust/src/print.rs
+++ b/examples/rust/src/print.rs
@@ -1,11 +1,11 @@
 #![no_main]
 
 #[link(wasm_import_module = "env")]
-extern "C" {
+unsafe extern "C" {
     fn printi32(x: i32);
 }
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub unsafe extern "C" fn add_and_print(lh: i32, rh: i32) {
     printi32(lh + rh);
 }
diff --git a/examples/rust/src/tinywasm.rs b/examples/rust/src/tinywasm.rs
index c3bf2d2..d3b3f8c 100644
--- a/examples/rust/src/tinywasm.rs
+++ b/examples/rust/src/tinywasm.rs
@@ -2,11 +2,11 @@
 use tinywasm::{Extern, FuncContext};
 
 #[link(wasm_import_module = "env")]
-extern "C" {
+unsafe extern "C" {
     fn printi32(x: i32);
 }
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn hello() {
     let _ = run();
 }
diff --git a/examples/rust/src/tinywasm_no_std.rs b/examples/rust/src/tinywasm_no_std.rs
index 9a31d20..46f1785 100644
--- a/examples/rust/src/tinywasm_no_std.rs
+++ b/examples/rust/src/tinywasm_no_std.rs
@@ -16,11 +16,11 @@ static ALLOCATOR: AssumeSingleThreaded<FreeListAllocator> =
     unsafe { AssumeSingleThreaded::new(FreeListAllocator::new()) };
 
 #[link(wasm_import_module = "env")]
-extern "C" {
+unsafe extern "C" {
     fn printi32(x: i32);
 }
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn hello() {
     let _ = run();
 }
@@ -30,7 +30,7 @@ fn run() -> tinywasm::Result<()> {
     let mut imports = tinywasm::Imports::new();
 
     let res = tinywasm::parser::Parser::new().parse_module_bytes(include_bytes!("./print.wasm"))?;
-    let twasm = res.serialize_twasm();
+    let twasm = res.serialize_twasm()?;
     let module = tinywasm::Module::parse_bytes(&twasm)?;
 
     imports.define(